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Mechanics Of The Car Jack

Shown above on the left is a plot of the change in height of the top plate with a linear change in distance between the left and right pivot. This shows how non linear the system is under usage.

The plot on the right shows the force between the left and right pin that would be applied to the threaded rod under 1000lbs of downward loading. It can be seen that when the jack is in its mostly closed state a much larger force must be applied to the thread to raise the 1000lb load. Under normal conditions the pinch weld of a car is approximately 4 inches off the ground. By this point the system has reached a linear portion of its travel and becomes easier for a person to operate.

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